There is conventionally known refrigerant circuitry of an air conditioner with two refrigerant circuits, for example, as disclosed in Japanese Patent Application Laid-Open Gazette No. 62-238951. The refrigerant circuitry of this type has a primary refrigerant circuit formed such that a compressor, a first heat source-side heat exchanger, a pressure reduction mechanism and a first user-side heat exchanger are sequentially connected through refrigerant piping, and a secondary refrigerant circuit formed such that a pump, a second heat source-side heat exchanger and a second user-side heat exchanger are sequentially connected through refrigerant piping. Heat exchange is made between the first user-side heat exchanger of the primary refrigerant circuit and the second heat source-side heat exchanger of the secondary refrigerant circuit. The second user-side heat exchanger is placed in a room to be air-conditioned.
In the air conditioner, during the operation of cooling the room, heat is exchanged between refrigerant evaporated in the first user-side heat exchanger and refrigerant condensed in the second heat source-side heat exchanger, and the condensed refrigerant is then evaporated in the second user-side heat exchanger to cool the room.
On the other hand, during the operation of heating the room, heat is exchanged between refrigerant condensed in the first user-side heat exchanger and refrigerant evaporated in the second heat source-side heat exchanger, and the evaporated refrigerant is then condensed in the second user-side heat exchanger to heat the room.
Thus, the piping length of the primary refrigerant circuit is reduced thereby enhancing refrigerating capacity.
In the secondary refrigerant circuit of the air conditioner above-mentioned, however, the pump is required as a drive source for refrigerant circulation. This invites inconveniences such as increase in power consumption. Further, the addition of the drive source increases the number of failure sites. This incurs an inconvenience of degraded reliability of the overall device.
As a device capable of eliminating the above inconveniences, there is a heat transfer device with no drive source in the secondary refrigerant circuit, commonly-called non-power heat transfer type heat transfer device, as disclosed in Japanese Patent Application Laid-Open gazette No. 63-180022.
In such a heat transfer device, the secondary refrigerant circuit is configured such that a heater, a condenser and a hermetically sealed enclosure are sequentially connected through refrigerant piping. The hermetically sealed enclosure is placed at a higher position than the heater. Further, the heater and the hermetically sealed enclosure are connected through a pressure equalizing pipe having a shut-off valve.
In the above heat transfer device, during the operation of heating the room, the shut-off valve is first closed, gas refrigerant heated in the heater is condensed in the condenser so as to be liquefied, and the liquid refrigerant is recovered to the hermetically sealed enclosure. Thereafter, the shut-off valve is opened so that the heater and the hermetically sealed enclosure is equalized in pressure through the pressure equalizing pipe. Thereby, the liquid refrigerant is returned from the hermetically sealed enclosure located at the position higher than that of the heater to the heater. In a manner that such an operation is repeated, refrigerant circulates in the secondary refrigerant circuit without the need for providing a drive source such as a pump in the secondary refrigerant circuit.